The present invention relates generally to hand level instruments having bubble vials mounted thereto, and more specifically to such a hand level instrument for which the various working surfaces are made from metal, while the remainder of the body, including critical interactive portions of the tool, is made from injection molded plastic.
Hand level instruments like combination squares provide a versatile tool for the craftsman. Formed from a plurality of parts, they commonly provide a blade having a ruled surface for measuring linear distances and scribing straight lines, a handle which interacts with the blade to define 90.degree. and 45.degree. angles, and a bubble vial mounted in the handle portion thereof to define an angled relationship between the surface of the handle and a workpiece.
Traditionally, such combination squares have been made from metal, having a die-cast handle portion formed from zinc. While such an all-metal tool is rugged and provides metal working surfaces for scribing, it is relatively heavy. Moreover, casting metal in a die is a relatively expensive process, particularly where close tolerances are required, thereby adding the high costs associated with the die to the cost of the metal material, itself.
As an alternative, manufacturers have resorted to combination squares made entirely from plastic. While cheaper to manufacture, such squares are not as durable as ones made from metal, and do not provide metal working surfaces.
Efforts have been made to fashion hand level instruments from a composite of metal and plastic materials. For example, U.S. Pat. No. 3,921,306 issued to Provi discloses a carpenter's and mason's hand level having metal rails defining the corners (and therefore the work surfaces) of the level instrument joined by a metal cross web. Plastic material is injection molded around the cross web of the metal frame to complete a rectangular slab body for the tool. However, Provi uses the plastic filler material simply to reduce the amount of metal that must be used, and therefore the weight of the tool. No effort has been made to provide an integral, precision molded vial mounting for the bubble vial, nor is there any teaching regarding the use of a molded plastic matrix to provide precision interactive surfaces between the handle and blade portions of a combination square.